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• Evaluating of soil sulphur forms changes in long-term field experiments of Látókép

  71-76

  Evelin Kármen Juhász

  Andrea Balláné Kovács

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  The aim of this work was to evaluate the changes of different sulphur forms (soluble, adsorbed) in chernozem soil in a long-term field experiment supplied with increasing doses of NPK fertilizers for a long time. In addition, other objective of this study included the examination of the applicability of recommended extractants of the different sulphate fraction in Hungarian soils. A long-term field experiment was established at the Research Station of Látókép of the University of Debrecen in 1984. In addition to control, two levels of NPK fertilizer doses have been used with irrigated and non-irrigated variants. Winter wheat and corn were cropped in a crop rotation on plots. Soil samples were collected in three different development stages of winter wheat, at the stage of stem elongation (April), flowering (May) and ripening (June of 2018) from the topsoil (0–20 cm) of experiment plots. Water-soluble inorganic sulphate was extracted with 0.01M CaCl₂ solutions. The soluble plus adsorbed sulphate was extracted with 0.016M KH₂PO₄ solution. Sulphate was measured by turbidimetric method. 0.01M CaCl₂-SO₄^2— ranged between 0.293–1.896 mg kg^-1 and the 0.016 M KH₂PO₄-SO₄^2- varied between 5.087–10.261 mg kg^-1. The values of KH₂PO₄ SO₄^2- was higher than that of CaCl₂-SO₄^2-, because KH₂PO₄ extracted the adsorbed and soluble fractions of sulphate, while CaCl₂ extracted the soluble sulphate fraction. The amount of absorbed sulphate was calculated by the differences of KH₂PO₄- SO₄ and CaCl₂-SO₄. The KH₂PO₄ characterizes mainly the adsorbed sulphate fraction much more than the water-soluble fraction. KCl is the most widely used extractant for the determination of plant available sulphate content of soil in Hungary; therefore, KCl-SO₄^2- fraction also was determined. The KCl-SO₄^2- ranged between 0.328–2.152 mg kg^-1. The CaCl₂-SO₄^2- and KCl-SO₄^2- fractions were compared and based on Pearson's linear correlation, moderate correlation was established (r=0.511) between them. In all three extractant (0.01M CaCl₂, 1M KCl, 0.016 M KH₂PO₄) higher sulphate fractions were measured in the fertilized plots where superphosphate had been supplied for ages until 2010. The arylsulphatase activity of soil also was determined and ranged between 9.284 and 26.860 µg p-nitrophenol g^-1 h^-1. The lowest value was observed in the treatment with highest NPK2 dose, both in irrigated and non-irrigated areas.